The ability to thermally shape and form thin glass sheets is increasingly relevant to various industries. By way of a non-limiting example, the production of glass panes for automobiles is a complex process, which is constantly changing due to increasingly stringent environmental and safety requirements. The demand for intricate glass shapes with high optical quality and low weight is growing as governmental regulations require increased fuel economy and reduced emissions. The ability to make automotive parts from thinner glasses may translate to lower vehicle weight, improved fuel economy, reduced emissions, and/or improved vehicle weight distribution (e.g., lower center of gravity).
Prior art methods for shaping glass include placing glass sheets on a shaping mold, conveying the glass through a furnace to uniformly heat and soften the sheets, and allowing the softened glass to sag under gravity to assume a desired shape. The shaping mold serves as a surface around which the glass sheet can be formed to the desired shape. Such conventional shaping systems may work well with traditional glasses, which are thicker, such as glasses having a thickness ranging from greater than about 3 mm to about 6 mm. Thicker glass sheets can generally undergo viscous deformation while avoiding what is known in the art as the “bathtub effect,” where the edges of the glass show a steep falloff and the center is flat.
However, when thinner glasses (e.g., having thicknesses less than about 2-3 mm) are processed using these traditional methods, the glass tends to distort and stretch, which leads to excessive viscous thinning at the edges and the falling away of the bulk center of the glass under the gravitational load as well as undesirable wrinkling around the edges. Bending of large thin sheets of glass to form automobile parts such as roof panels, windshields, etc., may necessitate the establishment of a large temperature differential between the edges and the center of the glass.
Shaping of large thin sheets of glass may be performed in a lehr that is comprised of a number of furnaces arranged in series in which the temperature of the glass sheet is gradually raised to accomplish sagging under gravity. However, the temperature differential to achieve the desired shape for thin glasses cannot be accomplished with simple variable heating in the furnace due to radiation view factors from the hot and cold zones of the furnace walls to both the center and edges of the glass. Additional means are needed to block radiation, e.g., radiation from the hot furnace zone to the glass edges and from the cold furnace zone to the center of the glass. Heat shields and/or heat sinks can be used to block or absorb radiant heat along the glass edges. However, this solution may not be satisfactory for bending thin glass sheets for a variety of reasons, including undesired heat transfer across the glass sheet and a gradual loss of effectiveness of the heat shield as it heats up during the bending process. Moreover, heat shields can be bulky, cumbersome, and can add complexity and/or cost to the glass shaping operation.
Accordingly, it would be advantageous to provide methods and systems for shaping and tempering thinner glass sheets, more specifically a system that is able to establish a sufficient temperature differential between the edges and the center of a thin glass sheet. To reduce manufacturing costs and/or processing times, it may additionally be advantageous to provide a system that can function, at least in part, in conjunction with existing systems for bending and tempering traditional (e.g., thicker) glasses.